Social networking sites such as Facebook could raise your risk of serious health problems by reducing levels of face-to-face contact, a doctor claims. Emailing people rather than meeting up with them may have wide-ranging biological effects, said psychologist Dr Aric Sigman. Increased isolation could alter the way genes work and upset immune responses, hormone levels and the function of arteries. It could also impair mental performance. This could increase the risk of problems as serious as cancer, strokes, heart disease and dementia, Dr Sigman says in Biologist, the journal of the Institute of Biology. Social networking sites such as MySpace and Facebook allow people to keep in touch with friends over the web. They can swap pictures, play games and leave messages which explain how their day is going. But even though they are designed to bring people together, Dr Sigman said they were actually playing a significant role in people becoming more isolated